U.S. Pat. No. 7,498,968 (incorporated by reference herein) describes a synthetic aperture radar (SAR) system that is capable of forming high-resolution SAR images at near video rates, e.g., many times a second. The rate of image update allows users to determine when moving targets start moving, when and where they stop, the direction of motion, and how fast they are moving. Further, the radar shadows of moving targets can be used to determine the position and identity of the targets (including even slow moving targets), and display the target motion from frame to frame. SAR systems and techniques such as described in U.S. Pat. No. 7,498,968 are also referred to herein generally as “VideoSAR”.
A VideoSAR movie is a sequence of individual SAR images. The video product produced by VideoSAR is typically either a clip or a stream of images. A VideoSAR clip product is a file containing a closed set of SAR images, for example, thousands of SAR images captured over a few minutes. A VideoSAR stream product may be a true real-time video constructed as a sequence of SAR images
One application of Video SAR is the observation of shadows from moving objects. Fine azimuth resolution SAR images provide high quality detail of stationary objects, but shadows of moving objects often disappear. Coarse azimuth resolution SAR images provide dark shadows of moving objects, but with less detail of stationary objects. The darkness of the shadow from a moving object in a SAR image is a function of the percentage of the aperture time that the stationary clutter behind the object was obscured by the object. Coarse azimuth resolutions have shorter aperture times, which give darker shadows of moving objects. However, coarse azimuth resolution SAR images do not provide much detail of the stationary background clutter. On the other hand, fine azimuth resolution SAR images provide detail of the background clutter, but the shadows of moving objects are often very faint.
It is desirable in view of the foregoing to provide for producing a SAR image that shows distinct shadows of moving objects while preserving detail in stationary background clutter.